Hazardous waste disposal

ABSTRACT

Contaminated glycol is refined by vacuum distillation. Specifically the evaporator is heated to a temperature below the degradation temperature of the glycol. The vacuum is used to bring the flashpoint down sufficiently so that glycol evaporates or flashes at that temperature. The glycol is condensed and filtered through activated granular carbon. The principal use of refining the glycol is to refine the triethylene glycol used in natural gas dehydration plants. For such purposes the equipment is mounted upon a trailer to be taken to the plant for cleaning glycol. In such instance, in addition to refining the glycol, a cleaning agent (which contains a degreaser) is added to the refined glycol. The glycol is refined while the natural gas dehydration plant is in normal operation and therefore it is not necessary to stop the natural gas dehydration plant for refining the glycol used therein. In addition, by the addition of the cleaning agent, the dehydrating plant equipment may be cleansed of hazardous waste. The hazardous waste will be separated and concentrated in the distillation. Therefore, the transportation of the hazardous waste to a disposal location is simplified.

CROSS REFERENCE TO RELATED APPLICATION

This is a Division of U.S. patent application Ser. No. 09/205,496 filedDec. 3, 1999, entitled STRUCTURE FOR REFINING GLYCOL IN A NATURAL GASDEHYDRATION PLANT, which is now U.S. Pat. No. 6,080,280 issued on Jun.27, 2000; which was a Division of U.S. patent application Ser. No.08/886,793 filed Jul. 1, 1997, entitled GLYCOL REFINING, which is nowU.S. Pat. No. 5,882,486 issued on Mar. 16, 1999.

Applicant filed a Provisional Application on this subject matter on Oct.18, 1996, Serial No. 60/028,694, John W. Moore, Jr., invention forTriethylene Glycol Refining. Specific reference is made to thatdocument.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to recycling of fluids which have been pollutedor contaminated. The majority of the fluids treated according to thisinvention are used in natural gas treating plants, primarily TriethyleneGlycol (also called TEG). In addition, ethylene glycol and diethyleneglycol, which find use as anti-freeze, also accumulate hazardousmaterial and are recycled by this process.

Operators of natural gas dehydration and treatment plants will haveordinary skill in this art.

(2) Description of the Related Art

Natural gas flowing from wells may contain water vapor, liquid water,brine solution, heavy and light hydrocarbons, and particulate mattersuch as sand, pipeline scale and rust. If these elements remain in thegas stream they will cause numerous problems in the pipeline andprocessing equipment. Treating natural gas will commonly occur atindividual wells, gathering systems, compressor stations, distributionstations, and gas processing units. Lowering the water content ofnatural gas at these sites will prevent the clogging of pipelines due tohydrate formation. Hydrate formation will occur with the combining ofwater and natural gas molecules. Hydrates will block valves andflowmeters. Hydrates will also accumulate at low points in the pipeline.Hydrates will decrease pipeline efficiency and cause shutdowns. Thehydrates will also increase erosion and corrosion. To prevent theformation of hydrates, natural gas must be dehydrated at theaforementioned sites prior to reaching the pipeline.

Processes for removal of entrained water vapor and other contaminants innatural gas are well known. The most common process for the removal ofwater in natural gas is glycol dehydration. The process is done in anatural gas dehydration plant. Where TEG is the preeminent desiccantused in the dehydration process. TEG offers the following advantages: 1)ability to absorb large amounts of water, 2) relatively low solubilityof valuable gas constituents, 3) chemical stability, 4) easy toregenerate, and 5) low cost. Before treating natural gas with glycoldehydration, the wet natural gas passes through an inlet separator wherewater droplets, liquid hydrocarbons, entrained sand, rust and so forthare separated out of the gas stream. The wet natural gas then flows tothe absorber or contacting tower where it is interfaced with the TEG.The wet natural gas will enter the contacting tower at the bottom whereit will flow upward, while lean TEG, free of water, will enter the topof contacting tower where the TEG flows downward. The counter currentflow will aid the lean TEG in absorbing most of the water contained inthe natural gas. The natural gas stream leaving the tower is said to bedehydrated. The TEG leaving the tower is called rich TEG. The rich TEGis passed through sock filters to remove any particulate matter pickedup by the TEG. The rich TEG then flows to a reboiler or regeneratorwhere it is heated to drive off any of the absorbed water contained inthe rich TEG solution. After the TEG has been regenerated, it is thenrecycled-for reuse in the dehydration system. The TEG is recirculatednumerous times per hour through the entire dehydration system(absorbertower and regenerators).

In normal use a supply of TEG will run for several months before it getsso laden with impurities that it is no longer efficient to continue use.Many of the contaminants are hazardous materials requiring expensivelimitations upon their disposal. This refining unit is preferablymounted on a trailer so that it may be moved to a dehydration systemwhere it is needed to refine or purify the spent TEG and return it tostorage for reuse. The TEG can also be used to clean the dehydrator.Those in the art will understand that the dehydrators become loaded withcontaminants which are hazardous, which in turn, requires expensivedisposal. However, with this process, the TEG can be circulated throughthe dehydrator system and greatly reduce the volume of materialrequiring disposal.

For background information relating to glycol dehydration systems fortreating natural gas, reference may be had to U.S. Pat. Nos. 5,163,981;5,116,393; 4,375,977 and 4,661,130.

The problems encountered with TEG dehydrators is that along with water,the TEG starts to pick up small amounts of light liquid hydrocarbons.These hydrocarbons are not as easily removed as the water in theregeneration phase and a certain amount of the hydrocarbons remain withthe lean TEG as it circulates back through the absorber column. Thehydrocarbons attract other contaminants along with more hydrocarbonsthat are found in the gas stream and the TEG becomes further dilutedwith pollutants. As the TEG becomes more saturated, contaminants andhydrocarbons are increasingly more difficult to remove in theregeneration process. Some aromatic hydrocarbons are passed along withthe water vapor into the atmosphere. These aromatic hydrocarbons areconsidered pollutants. They include benzene, toluene, ethylene andxylene, commonly known as BTEX. They are environmentally hazardous andconsidered carcinogens. These and other hydrocarbons that may begenerated in the process of dehydrating natural gas are referred to asvolatile organic compounds(VOC). The control of BTEX and other VOCemissions from TEG dehydration units is of increasing concern toenvironmental protection both at the federal and state levels. Airquality regulations in the United States are increasing because of theClean Air Act Amendments (CAAA) of 1990. Other regulations include theNational Emission Standard Hazardous Air Pollutants (NESHAP) program andstate regulatory agencies.

Another source of contamination to the TEG system is salts. Carry overof brine solutions from the field can lead to salt contamination in theTEG system. Sodium salts (typically sodium chloride) are a source ofproblems in the reboiler since sodium chloride is less soluble in hotTEG than in cool TEG. Salts will precipitate from the solution attypical reboiler temperatures of 350 to 400 degrees Fahrenheit atatmospheric pressure. The salt can deposit on the fire tube restrictingheat transfer, causing the temperature of the fire tube increase, whichwill lead to thermal degradation of the TEG. The salt will also increasecorrosion of the fire tube. The dissolved salts cannot be removed bymechanical filtration. When the salt content reaches 1% the TEG is spentand should be reclaimed or replaced.

After a period of time, the TEG becomes severely contaminated and losesits effectiveness as a desiccant and is considered “spent”. TEG at 94%concentration in solution becomes increasingly ineffective as adesiccant. The presence of contaminants may result in fouled equipment,foaming, poor dehydration and the potential of increased release ofpollutants into the atmosphere. The options for spent TEG are to disposeof it and replace it with new TEG. The spent TEG may also be sent to areclaimer for recovery. (Both of which are not very economic and willrequire the dehydration system to be shutdown.) During these down timesoperators currently choose to clean the dehydration system atconsiderable costs, which produces large amounts of hazardous waste tobe disposed of. This also increases the chance of spilling the hazardouswaste onto the ground causing more problems.

SUMMARY OF THE INVENTION

(1) Progressive Contribution to the Art

According to this invention, the glycols may be cleaned and recycled byvacuum distillation. The glycols have an evaporation temperature atatmospheric pressure higher than the temperature at which theydegenerate. It is necessary to evaporate them at a temperature below thepoint that they degenerate. The evaporation temperature is elevated ashigh as possible but still must be below the degeneration point. Theabsolute pressure is reduced on the evaporating liquids on a economybasis. The absolute pressure is reduced as low as possible for rapidevaporation and temperatures no higher than necessary. However, toobtain extremely low absolute pressures is difficult and expensive.Therefore the pressure used for evaporation is one that is a balancebetween these considerations.

An improved process of refining TEG is provided in which the unit is amobile self contained unit that will purify the spent TEG bysubstantially reducing the amount of entrained solids and hydrocarbons.The refining unit can also be used to clean contacting towers, heatexchangers, pumps, still column, reboiler and surge tanks of TEGdehydrators. This will provide a 97% volume reduction in hazardouswastes compared to conventional methods of cleaning dehydrators. Theunit accomplishes this with vacuum distillation incorporating a closedsystem. The refining unit utilizes the TEG located at the site alongwith a chemical degreaser that aids in the removal of coke and sludgebuildups. All contaminants and foulants that are removed from thecontacting tower of the dehydration system are removed by the refiningunit. The unit eliminates the risk of hazardous waste spills thatcommonly occur with conventional cleaning methods of dehydrationsystems. All wastes that occur during cleaning and refining are gatheredin the refining unit. These wastes can be collected very easily to bedisposed of properly. The refining unit will provide efficient cleaningof dehydration equipment, reduce hazardous waste volume, converthazardous waste into a useful product, reduce the emission of dangerousVOC's and BTEX all without shutting in gas sales. The refining unit isable to accomplish this since it is a closed system. The unit canutilize dehydrated gas or LPG at the site for fuel gas for the burner,power medium used in the operation of valves, shutdowns and fluidtransfer.

The refining unit is kind to the environment by utilizing spent solutionin a cleaning process, returning a spent solution to its usable form,recycling spent solution which eliminates the need to produce moresolution, eliminating the emission of hazardous VOC's and BTEX duringrefining, reducing the emission of VOC's and BTEX in TEG dehydrationunits, reducing hazardous waste that can be created during a cleaningoperation, eliminating the risk of soil contamination due to hazardousspills, simplifies the collection of hazardous waste at the site andaccomplishing all of the aforementioned while the dehydration systemcontinues gas sales.

This invention also is used to recycle glycols used as anti-freeze. Itis more economical to gather the used anti-freeze and transport it to astationary recycling plant.

This invention reduces if not completely prevents the release of BTEXgases into the atmosphere. This invention reduces by 97% the amount ofhazardous waste from the polluted glycol. It eliminates the addedindustrial hazard of the conventional cleaning of the polluted gas plantequipment. The normal cleaning of the equipment greatly increases thevolume of the hazardous waste; making up to five times as much hazardouswaste as originally present because of the volume of the pollutedcleaning fluid. The immediate vicinity is protected by the use of acompletely closed system.

This process has the following unique features and advantages:

(1) To purify the TEG with the unit requires only one cycle.

(2) Self containment of the TEG refining process, hydrocarbon adsorptionprocess and dehydration system cleaning process, thus the equipment ofthe refining unit may be mobile.

(3) Process that reduces a contaminated waste product to the lowestpossible volume for disposal while purifying TEG and cleaningdehydration systems.

(4) Recycles contaminated TEG instead of the disposing of contaminatedTEG and replacing with new TEG at approximately 50% of the replacementcosts.

(5) Reduces disposal of hazardous waste by over 95%.

(6) Allows user to produce natural gas uninterrupted while purifying TEGin the refining unit.

(7) Allows user to produce natural gas uninterrupted while cleaning thedehydration system.

(8) Reduces waste disposal generated while cleaning dehydration systemfrom 100% to 1% by volume.

(9) Does not emit hazardous VOC's and BTEX.

(10) Provides the process in closed system eliminating the risk ofhazardous waste spills.

(11) Helps reduce hazardous air emissions from dehydrator units.

(12) Improves gas/glycol contacting resulting in better water removal.

(13) Eliminates foaming stopping uncontrolled glycol losses.

(14) Reduces the risk of salt contamination in the dehydration systemwhich can cause hot spots on the fire tube, thermal degradation of theTEG and increase corrosion in the dehydrator system.

(2) Objects of this Invention

An object of this invention is to recycle glycols for reuse.

Another object of this invention is to recycle glycol from a natural gasdehydration plant and simultaneously clean the equipment of the naturalgas plant to both rejuvenate the glycol and to concentrate and removethe hazardous waste from the natural gas plant.

A further object of this invention is to recycle glycols used asanti-freeze.

Further objects are to achieve the above with devices that are sturdy,compact, durable, lightweight, mobile, simple, safe, efficient,versatile, ecologically compatible, energy conserving, and reliable, yetinexpensive and easy to manufacture, install, operate, and maintain.

Other objects are to achieve the above with a method that is rapid,versatile, ecologically compatible, energy conserving, efficient, andinexpensive, and does not require highly skilled people to install,operate, and maintain.

The specific nature of the invention, as well as other objects, uses,and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawings, the different views ofwhich are not necessarily scale drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow schematic diagram of the glycol refining process inwhich the present invention is embodied.

FIG. 2 is a schematic of the trailer.

CATALOGUE OF ELEMENTS

As an aid to correlating the terms of the claims to the exemplarydrawing(s), the following catalog of elements and steps is provided:

9 source of contaminated glycol solid line = glycol 10 conduit 11 checkvalve irregular dash lines = 12 inlet control valve cleaning agent 13surge tank 14 valve 15 gate valve dashed lines = natural 16 line gas 17heating coil 18 pump valve 19 vacuum reboiler or evaporator 20 burner 22pre-condense air cooler 25 wye-strainer 27 vacuum pump 28 wye strainer29 air cooler 31 seal oil tank 33 transfer pump 35 particle filter 36carbon filter 37 outlet line 38 bypass line 39 temperature switch 40burner supply valve 41 pilot regulator 42 pilot line 43 burner supplyline 44 float switch 45 pump float switch 46 two-way valve 47 pressureregulator 48 inlet line 49 temperature switch 50 seal oil cooler 51regulator 52 vapor chamber 53 gas accumulator 54 chemical injection tank55 ball valve 60 trailer 62 base structure 64 wheels 66 trailer hitch 68storage tank

DESCRIPTION OF THE PREFERRED EMBODIMENTS(S)

When used with a natural gas dehydration plant this invention isdesigned to remove impurities from TEG.

Referring to FIG. 1 there is shown a schematic flow sheet showing theequipment for the glycol refining process embodying the presentinvention. The processing of the contaminated glycol can be conducted ona batch or semi batch process. Spent TEG is brought into the system byvacuum and/or gravity. The natural gas dehydration plant 8 is a source 9of contaminated TEG for the refining equipment. The spent glycol entersthe system in a conduit 10 that then passes through a check valve 11.The spent glycol then flows through the inlet control valve 12 and intothe surge tank 13. The inlet control valve 12 is controlled by high andlow level shutdowns located in vacuum reboiler or evaporator 19 and sealoil tank 31. When a low or high level shutdown occurs the inlet controlvalve 12 is shut and a temperature switch 49 cuts off the fuel supply toburner 20.

After the spent TEG is received in the surge tank 13 it then passesthrough a gate valve 15 into line 16. The spent TEG then passes througha heating coil 17 located inside the vacuum reboiler 19. The spent TEGthen flows through dump valve 18, where the level inside the vacuumreboiler 19 is controlled by a float switch 44. When the float switchindicates that additional spent TEG is required in the vacuum reboiler19 the dump valve 18 opens. The dump valve 18 remains open until thefloat switch 44 is tripped and the dump valve 18 is closed.

Supply gas is used to operate pressure regulator valves, and “pump” TEGfrom transfer pump 33 (as described later) as well as to fire the burner20 and “pump” cleaning chemical from chemical injection tank 54 to thedehydration system. The source of the supply gas may be methane from thedehydration plant or from bottled liquid petroleum gas (LPG) such aspropane.

The supply gas enters the system through inlet line 48 where the supplypressure is set by regulator 47. The supply gas is then passed throughseal oil cooler 50 which aids in vaporizing the LPG if used.

Fuel to the burner 20 is supplied by regulator 51 where the fuel passesthrough burner supply valve 40 to burner supply line 43. The temperaturein the evaporator vacuum reboiler 19 is maintained at about 400 degreesFahrenheit. This is accomplished by the reboiler temperature switch 39.The pilot gas for the burner 20 is supplied through a regulator 41 topilot line 42.

A burner with a flame tube submerged in the spent glycol is used to heatthe vacuum reboiler. The boiler is sufficiently sized to provideadequate retention time to allow the suspended solids to settle out bygravity acting as a settling basin. The small amount of sludge that willbe produced in the bottom of the vacuum reboiler must be removed anddisposed of as hazardous waste.

The spent TEG is flashed as it is heated at 400 degrees Fahrenheitwithin the vacuum evaporator or reboiler 19 while being subjected to avacuum of 20-22 inches of mercury or an absolute pressure of about 9inches Hg. The vapors that are produced are removed through vaporchamber 52 of the vacuum reboiler 19. The vapors then pass throughpre-condense air cooler 22. The vapors are cooled within the air cooler22 to a temperature so that about 30% of the vapors are condensed beforethey enter vacuum pump 27. The vacuum pump 27 provides the desiredvacuum. A manually controlled throttle valve on the pump allows theoperator to adjust the vacuum. The vacuum may vary over a range of +/−7inches of mercury. A Wye (or Y)-strainer 25 is located before the vacuumpump 27 to remove any scale that may remain in the condensed TEG.

The partially condensed vapors from the vacuum pump are then passedthrough another air cooler 29 where the vapors are completely condensedand then stored in the seal oil tank 31. A small amount of the condensedTEG will be used as seal oil for the vacuum pump 27. The seal oil ispulled by vacuum to the vacuum pump 27 from the seal oil tank 31,through the air cooler 50. The cooling of the seal oil is furtherenhanced by passing the supply gas through the air cooler 50. The sealoil is then passed through a Y-strainer 28 to the vacuum pump 27. Theseal oil is used to seal the ends of the vanes against the housing onthe turbine type vacuum pump 27.

Liquid TEG from the seal oil tank 31 flows by gravity to the transferpump 33. As TEG accumulates in the transfer pump 33, a float switch 45located inside the transfer pump 33 will actuate the two-way valve 46.This will pressurize the transfer pump 33 and disperse any fluidcontained. As the transfer pump 33 begins to empty it will trip thefloat switch 45 again actuating the two-way valve 46 and venting thetransfer pump 33 207 to atmosphere. The transfer pump 33 will againallow TEG to accumulate until the float switch 45 is tripped again.Supply gas used in powering the transfer pump 33 is stored in a gasaccumulator 53. The transfer pump 33 forces the TEG through particlefilter 35, granular activated carbon filter 36, and outlet line 37 to aclean TEG storage tank 68.

The solution then passes through a granular activated carbon filter thatwill remove any BTEX, VOC's, hydrocarbons, surfactants, well treatingchemicals, compressor lubricants and TEG degradation products. Theadsorption process is more effective after the vacuum dehydration andrecondensing of the solution. The vacuum process allows the unit toconduct a reversible adsorption process on the TEG by adsorbing thedissolved hydrocarbons.

The particle filter 35 is used to remove any entrained solids or scale.The granular activated carbon filter 36 is used to remove anyhydrocarbons. This is the final step in the refining process and thefinished product may be returned to the dehydrating system via the cleanTEG storage tank.

When it is necessary for the dehydrating system to be cleaned thepurified TEG may be used. The condition of the dehydration systemequipment may be determined by visual and laboratory inspection ofincoming glycol sampled at valve 14. A chemical injection tank 54 isprovided on the refining unit to assist in the cleaning process. Thechemical injection tank 54 is pressurized using the supply gas. The TEGand cleaning chemical is circulated through the dehydrating unitcontinuously until the dehydrating unit is cleaned. The TEG and cleanerwill remove sludge and coke build up in the dehydration system. The TEGthat is circulated will become contaminated and will be returned to theTEG refining unit. The cleaning process will be done continuously untilboth the TEG and dehydrating system are clean. All wastes that aredeveloped during cleaning are contained in the closed system so thatthey may be disposed of properly without the risk of spillage. Achemical injection tank is provided on the refining unit to enhance thecleaning process. The chemicals used in the refining unit are adegreaser and sometimes a water based cleaner. The cleaner is non-acidicand non-alkaline and is classified as a non-corrosive. The cleaner isonly slightly toxic to daphnia magna (water flea) and bacterialpopulations at concentrations well above those expected to beencountered. The degreaser is only moderately toxic to daphnia magna andfathead minnows and it is relatively noninhibitory to bacterialpopulations. Both the cleaner and degreaser biodegrade rapidly. Thedegreaser contains no volatile organic solvents, halogenated solvents,inorganic phosphates or other alkalinity builders. The cleaner, ifnecessary, removes all mineral scales, rust and other forms ofcorrosion. The degreaser removes all hydrocarbon based foulants. Whenthe hydrocarbon based foulants are removed, usually the othercontaminates are removed by clean glycol. Solution strengths range from5 to 25 volume percent depending upon the scale and foulants to beremoved from the dehydration system. The solution depletion is measuredby the pH and if the solution drawn at valve 14 remains at a constantvalue at or below 8 for an extended period the dehydration system isprobably clean. The operator cleans the unit on this basis and visualexamination and runs the cleaning cycle until the pH of the solutionremains steady at 8. The TEG can be refined as mentioned aboveafter thecleaning process is done free of all contaminants and returned to theclean holding tank where it is ready for reuse in the TEG dehydrationsystem. Both the refining and cleaning process can be done while thedehydration system remains in operation without shutting in gas sales.The TEG can then be passed through the granular activated carbon 36remove any hydrocarbons and then be placed in a clean storage tank.

The preferred cleaning agent if used is NORKOOL Industrial Heat TransferSystem Cleaner, N801, NORKOOL degreaser DG/E803 is the preferreddegreaser. Both products of Union Carbide Corporation, Danbury, Conn.and are available from the Houston, Tex. location of the Union CarbideCorporation. Both these products meet the requirement that they arenon-acidic and non-alkaline and also classified as noncorrosive and arereferred to as cleaning agents.

In the operation, a standard chemical injection system is used whichpermits a regulated flow of the additive to a measured amount of glycol.Such units are well known and commonly available on the market. In thisuse, the cleaning agents will be used anywhere from 5% of the volume ofglycol to as much as 25% of the volume of glycol. Stated otherwise thisis a ratio of one part of cleaning agent to 20 parts of glycol to asmuch as one part of cleaning agent to 4 parts of glycol.

Normally the degreaser would initially be used at about 10% (one partcleaning agent to ten parts glycol). With this use the glycol wouldcontinually be sampled as it entered the recycling unit, at valve 14. Ifthe glycol at this point had a pH of 8%, the treatment would becontinued and if no particular progress was noted, the amount ofcleaning agent per glycol could be increased till favorable results wereobserved. At the point when the pH of the entering glycol is below 8%and is clear and not changing, it will be considered that the unit hasbeen cleaned.

Both the cleaner N801 and the degreaser E803 are considered to becleaning agents as the term is used in this application. The need forthe degreaser will also be apparent if the glycol shows a above normalamount of hydrocarbons at the valve 14. Again in the use of thedegreaser, it may be used in any ratio, from 5% of the volume of glycolto as much as 25% of the volume of glycol.

Caution must be used in using an excessive amount of cleaning agent inas much a excessive release of the contaminants on the equipment of thedehydrator will cause operating problems with the natural gasdehydrating process.

Hazardous materials will collect in the bottom of the vacuum reboiler 19and will be removed through a ball valve 55. The hazardous sludge willbe removed by first heating the reboiler 19 to about 400 degreesFahrenheit at atmospheric pressure or higher. This will liquefy thesludge and force it out. The small amount of hazardous sludge will becollected and disposed of as hazardous material. Wye strainers 25 & 28will also require periodic cleaning and this very small amount of wasteshould also be disposed of as hazardous material.

The filter elements used in this invention will need to be replacedregularly to maintain solution quality. The granular activated carbon 36and particle filter 35 will constitute a solid waste requiring properdisposal.

Vacuum is supplied by means of an electric motor driven pump 27. This isthe preferred arrangement when electrical energy is conveniently andeconomically available. In some locations where it is necessary todehydrate natural gas, electrical energy is not available or, at least,is not available on economic terms. In this case a gas or gasolinedriven vacuum pump 27 may be used. An electric generator that is drivenby a natural gas engine may be used to provide electric power in remotelocations.

As set out above that the rejuvenation of the glycol in a natural gasdehydration plant maybe only required about once a year and also maytake no more than three or four days to rejuvenate the glycol. Thereforeit is desirable to have the equipment mobile so that it can be movedfrom one natural gas dehydration plant to another. To accomplish thisall of the references made to FIG. 2. There may be seen that all theequipment necessary to accomplish the dehydration, although notnecessarily shown in FIG. 2, may be mounted upon a trailer 60. Thetrailer will have a base structure or bed 62 upon which all of theequipment is mounted. The trailer will have wheel 64 and a trailer hitch66 so that it can be moved from one unit to another. When it is moved toa unit, the conduit 10 will be connected to the gas plant and the gasplant will serve as a source 9 of contaminated glycol for the refiningequipment mounted upon the base structure of the trailer. Also, theconduit 37 from the carbon filter 36 will be connected to thedehydration plant.

Although it is preferred that the equipment be mounted upon a trailer,those skilled in the art will understand that it could be also othertypes of mobile structures, for example, a skid loaded upon a flatbedtractor trailer to be moved from one location to another. Also othermobile structures might be used.

Also as stated above the unit is also useful in refining ethylene glycoland diethylene glycol which are used as anti-freezes. In such aninstance, it is more economical to bring the spent or contaminatedglycol to the refining unit. In this event, the refining unit might wellbe the equipment mounted upon a mobile structure which is located atsome convenient location. If the anti-freeze to be refined is ethyleneglycol it will be understood that the evaporator temperature can beabout 240° F. at which point the ethylene glycol will evaporate rapidlyat nine inches of Hg. absolute pressure. This adjustment of thetemperature of the evaporator can readily be made by the controls whichwould normally control its temperature at about 400°. Likewise if theanti-freeze was diethylene glycol the temperature of the evaporatorwould be about 255° F.

Also since the equipment is in place, it can be operated at a pressureof nine inches of Hg. absolute. As set out above that the amount ofvacuum which is pulled upon the evaporator is balance between thedifficulty of obtaining high vacuums and the convenience of operatingthe equipment at large volume and the constraints that the temperatureof the evaporator is limited by the degradation point of the glycolbeing refined. In this regard it is noted that there is about a +/−7p.s.i. variance so that the vacuum that the evaporator operates at forany of the glycols might vary from as low as 2 inches of Hg. absolute toas much as 16 inches Hg. absolute.

The embodiment shown and described above is only exemplary. I do notclaim to have invented all the parts, elements or steps described.Various modifications can be made in the construction, material,arrangement, and operation, and still be within the scope of myinvention.

While the invention has been described in relation to certain preferredembodiments, it is apparent to those skilled in the art that changes maybe made to the arrangement of the components and it is susceptible toadditional embodiments without departing from the basic principles ofthe invention.

The restrictive description and drawings of the specific examples abovedo not point out what an infringement of this patent would be, but areto enable one skilled in the art to make and use the invention. Thelimits of the invention and the bounds of the patent protection aremeasured by and defined in the following claims.

I claim as my invention:
 1. A method of removing hazardous wastes fromone of a group of contaminated glycols consisting of diethylene glycoland triethylene glycol which has been used in a natural gas dehydrationplant comprising steps of: a) flowing contaminated glycol from thedehydration plant to an evaporator b) evaporating the contaminatedglycol, by c) heating the contaminated glycol to a temperature below thetemperature at which the glycol degenerates, while d) reducing theabsolute pressure on the glycol, then e) condensing the evaporatedglycol, f) collecting unevaporated hazardous waste, g) disposing of theunevaporated hazardous waste, and h) returning the condensed glycol tothe dehydration plant.
 2. The method as defined in claim 1 furthercomprising: j) cleaning equipment of the dehydration plant by k) addinga cleaning agent to the glycol after step g) above and before step h)above, thereby l) removing contaminates from the equipment as well asfrom the natural gas.
 3. The method as defined in claim 2 furthercomprising: m) said glycol is triethylene glycol and the temperature ofstep c) is about 400° F. and the absolute pressure of step d) is about 9inches of Hg.
 4. The method as defined in claim 3 further comprising: n)the cleaning agent contains a degreaser.